Problem: William is 3 times as old as Vanessa and is also 20 years older than Vanessa. How old is William?
Explanation: We can use the given information to write down two equations that describe the ages of William and Vanessa. Let William's current age be $w$ and Vanessa's current age be $v$ $w = 3v$ $w = v + 20$ Now we have two independent equations, and we can solve for our two unknowns. One way to solve for $w$ is to solve the second equation for $v$ and substitute that value into the first equation. Solving our second equation for $v$ , we get: $v = w - 20$ . Substituting this into our first equation, we get the equation: $w = 3$ $(w - 20)$ which combines the information about $w$ from both of our original equations. Simplifying the right side of this equation, we get: $w = 3w - 60$ Solving for $w$ , we get: $2 w = 60$ $w = 30$.